There is conventionally known a clutch operation assisting device that uses an urging force, such as a spring force, for assisting in manual clutch engagement/disengagement operation (see, for example, Japanese Patent Publication 2005-326018). The clutch operation assisting device described in Japanese Patent Publication 2005-326018 is interposed between a clutch lever and a clutch and reduces the force required to operate the clutch lever.
As shown in FIG. 18a, the clutch operation assisting device described in Japanese Patent Publication 2005-326018 includes a compression coil spring 234 and a spring holder 253 that supports the compression coil spring 234 and expands or compresses in a longitudinal direction according to the compression coil spring 234. The base of the spring holder 253 is formed to pivot about a pivot support point C1 and a tip end of the spring holder 253 is connected to a lever 238 via a connection pin 241. The lever 238 is arranged in a drive force transmission system between the clutch lever and the clutch and rotates about a spindle 243. In FIGS. 18a to 18c, if the clutch lever is operated in a direction of disengaging the clutch, the lever 238 rotates clockwise. If the clutch lever is operated in a direction of engaging the clutch, the lever 238 rotates counterclockwise.
A so-called “play area”, in which a load from the clutch (hereinafter, “clutch load”) is not applied to the clutch lever even if the rider grips the clutch lever, is provided in the clutch. In the play area, even if the rider grips the clutch lever, the clutch is not disengaged. A position where the clutch starts to be disengaged is called a “meet point” (that is, “disengagement start position”). After the lever 238 exceeds the meet point, the clutch load is applied to the clutch lever. Accordingly, in the clutch operation assisting device, the assisting force of the compression coil spring 234 is zero at the meet point and acts in the direction of disengaging the clutch while the clutch lever is operated in the direction of disengaging the clutch after the lever exceeds the meet point.
Specifically, as shown in FIG. 18b, at the meet point, a line L1 connecting the pivot support point C1 of the spring holder 253 and a center of the connection pin 241 coincides with a line L2 connecting the pivot support point C1 to a center of rotation of the lever 238 (that is, the center of the spindle 243). Due to this, the assisting force of the compression coil spring 234 is zero.
As shown in FIG. 18c, while the lever 238 exceeds the meet point and moves toward the clutch disengagement side, the line L1 moves below of the line L2 and the biasing force of the compression coil spring 234 acts as an assisting force for rotating the lever 238 clockwise (that is, in the direction of disengaging the clutch).
On the other hand, as shown in FIG. 18a, in the play area, the line L1 deviates above the line L2 and the urging force of the compression coil spring 234 acts in the direction of rotating the lever 238 counterclockwise, that is, in the direction of engaging the clutch. As a result, the biasing force of the compression coil spring 234 acts as a force for applying a load to the rider who grips the clutch lever (hereinafter, “reverse assisting force”) in the play area. Therefore, a canceling compression coil spring 235 that applies a biasing force to the lever 238 when rotated within the play area is separately provided in the clutch operation assisting device so as to cancel the reverse assisting force.
As can be seen, the clutch operation assisting device is a device for assisting in the rider's manual clutch operation. On the other hand, devices for performing clutch disengagement and engagement operations using an actuator such as an electric motor (hereinafter, “clutch drive devices”) are also known. For example, Japanese Patent Publication 2007-069638 discloses a clutch drive device which includes a compression coil spring that generates the assisting force needed to lessen the load on the clutch actuator. This type of clutch drive device, however, also generates a reverse assisting force caused by the compression coil spring in a play area. Consequently, an unnecessarily excessive load is applied to the actuator in the play area. To lessen the load on the actuator, therefore, a canceling compression coil spring is separately provided in the clutch drive device. Separately providing the canceling compression coil spring in the clutch drive device, however, disadvantageously entails an increase in the number of components, a complicated structure, and a cost increase.